Let’s face it – ductwork isn’t exciting. But get it wrong on a commercial build, and you’ll be chasing problems long after handover. Too loud, not enough airflow, stuff not passing inspection – you name it.
Specifying ducting properly isn’t just about picking sizes from a chart. It’s about understanding what’s needed for the space, staying on top of fire safety, and making sure everything actually works once it’s installed.
If you’re responsible for getting the ductwork right – here’s what you want to think about before anything gets ordered or fitted.
What’s the Job of the Ductwork?
Start here. What’s the ducting actually doing?
Is it pulling stale air out of a kitchen? Pushing fresh air into a call centre? Extracting fumes from a print room?
Each of those setups needs a different approach. Some need grease-resistant ducting. Others need quiet runs. Some might require high airflow at low pressure. And some just need to tick fire safety boxes.
If you don’t define the job clearly from the start, you’ll end up with a one-size-fits-none system that no one’s happy with.
Getting the Size Right (and Not Guessing)
Sizing ductwork isn’t just about space – it’s about airflow. Move too little air, and things feel stuffy or hot. Move too much, and you’ve got noise, wasted energy, and unhappy building managers.
Here’s a simplified approach:
- Work out how much air you need to move (in litres per second or cubic metres per hour).
- Decide on an acceptable air velocity (too high = noise and energy waste).
- Match your duct size to those numbers.
Most people use software or a Ductulator, but even a basic spreadsheet helps. Just avoid the common trap of oversizing “just to be safe.” Bigger isn’t always better.
Material Choices (There’s More Than One Right Answer)
Galvanised steel is the workhorse – no surprise there. It’s strong, durable, and plays well with fire regulations. But it’s not your only option.
Depending on where the ducting is going, you might want to think about:
- Aluminium – easier to handle and won’t rust, good in humid areas
- PVC or plastic – decent chemical resistance, often used in specialist extract systems
- Flexible ducting – useful in tight spots, but keep it short and well-supported
And if you’re running ducting through cold spaces – like roof voids or plant rooms – insulation is a must. It stops heat loss, condensation, and helps keep energy costs under control.
Fire Safety: Not Just a Checkbox
This is the bit that can catch you out if you don’t check early. Ductwork that crosses between fire zones – say, through a wall or between floors – needs to maintain that barrier.
That might mean:
- Fire dampers
- Intumescent collars or wraps
- Fire-rated duct sections
- Smoke extract systems if the building design calls for it
Check with Building Control or your fire consultant early. You really don’t want to be retrofitting dampers after the ceilings are closed up.
Duct Shape, Layout, and Keeping It Simple
Here’s the deal: round ducts flow better. They’ve got less resistance and fewer leakage points. But sometimes you’re tight on space, especially above a suspended ceiling – and that’s where rectangular ducting makes sense.
Whichever you use, try to keep the layout as clean as possible. Every bend, junction, or reducer adds resistance. Every extra fitting means more potential for leaks or vibration.
If you’re dealing with long runs or lots of branching zones, build in:
- Dampers (for balancing)
- Access panels (for maintenance)
- Some common sense (e.g. don’t run return air right next to the staff kitchen)
What About Noise?
People forget this until someone complains.
Duct systems that carry air too fast – or come straight off a noisy fan – can create a real racket. In open-plan offices, meeting rooms, or residential builds, that’s a problem.
Here are a few ways to keep it quiet:
- Slow the air down (biggest fix)
- Use acoustic lining inside ducts near fans or AHUs
- Install attenuators in long runs or near outlets
- Isolate fans and heavy gear with anti-vibration mounts
And keep in mind: flexi ducts can vibrate and flap if they’re not properly fixed. Seen it too many times.
Sourcing Good Ducting Gear
This part gets overlooked until the last minute – and then everyone is scrambling to find elbows, reducers, or fire collars. And usually someone’s forgotten to order hangers or sealant.
Working with a reliable supplier like Ducting Express saves a lot of that grief. They’ve got stock ready for commercial jobs – spiral, pressed fittings, silencers, flexible hose, even fire-rated gear – and they deliver fast. If your site’s running tight, that can be the difference between hitting a deadline or not.
They also know what they’re talking about. You’re not just dealing with a generic trade counter – these guys work with HVAC contractors every day.
Final Word
Ductwork isn’t the flashiest part of the build – but it’s one of the most important. When it’s specified properly, you don’t hear about it again. Which, in construction, is a win.
Plan early. Think about airflow, fire safety, space, and access. Don’t overspec, but don’t guess either. And work with people who actually understand what a commercial site needs – not just what’s in stock.
Because once the ceiling tiles are in, the last thing you want is to be cutting them back out.
